My brother has a '98 XLT 4x4 ext. cab with the 5.4. His battery light has been coming on and staying on lately. We tested his battery and a couple of the cells were dead, so we went and got a new one. The light is still on!
Is there a way to reset the light or something?
Does anybody have any ideas of what the problem could be?
He has a radar dector and CB plugged in to the cig. lighters, but they are not always on, and rarely on together. He also has a system, but it has been the same for over 2 years, so we don't think that is the problem. The light os on wether the accesories are on or not. The light will sometimes go off for a few seconds, but then come right back on. The battery guage is reading fine and everything seems to be operating normally. His alternator is also fairly new.
He does have the common problem with the AC blowing through the defroster, but I doubt that has anything to do with it.
We're stumped.

 

Battery light with the engine running usually points to the alternator and Battery light with the engine not running usually means a battery problem.

I think some alternators have fuses mounted on the firewall of the truck. If you have them then test that the fuses are not blown.

 

Alternator is going bad.

 

Use a volt meter to check and see what the charging voltage is, sounds like a bad alt. Also have seen a poor connection on the connector on the alt cause the same problem.

 

We tested it and the alternator isn't charging the battery properly, so now it's at the shop because the alternator was replaced last year and it's got some kind of warranty. I'll post back when the cause is pin-pointed. Thanks guys!